Electric cable



Dec. 12, 1933. 1,939,264

ELECTRIC CABLE Filed Jan. 3. 1931 Fig. 1.

In M! BY 4 M' M' ATTORNE Patented Dec. 12, 1933 UNITED STATES ELECTRIC CABLE Harry Hill, London,

England, assignor to Callenders Cable and Construction Company Limited, London,

England, a British company Application January 3, 1931, Serial No. 506,375,

and in Great 5 Claims.

This invention relates to the manufacture of electric cables comprising paper insulation impregnated with suitable liquid or semi-liquid material (for instance, oil or compound, hereinafter for conveniencereferred to as oil). In accordance with the invention paper, treated in such a way as to make penetration by the oil easier in one sense than in the other, is utilized in the manufacture of the insulation. The treatment given to the paper aifects the fibrous structure locally at a number of points so as to provide a kind of valve action which permits an easier flow of oil from one side of the paper to the other than the flow in the reverse sense. To attain this result the paper is operated upon in such a way as to displace fibres grouped round a centre into positions which lie at an inclination with the normal plane of the paper. This treatment is given to the paper at a number of points distributed over its surface and it results in the loosening of the engagement between the fibres, at these places, permitting them to open out so as to facilitate flow through the paper in one sense whilst giving them a tendency to be closed by flow in the reverse sense.

The invention will be further described by the aid of the accompanying drawing in,which:

Fig. 1 is a plan on an enlarged scale of a piece of the treated paper, the magnification factor being of the order of ten and Fig. 2 is a fragmental section through the piece of treated paper taken on the line XX in Fig. 1, in this case the magnification factor is of the order of twenty.

Fig. 3 is a side elevation of a piece of cable showing the insulation and Fig. 4 is a section of the cable taken on the line Y--Y of Fig. 3.

Figures 1 and 2 illustrate one way in which the paper with the desired fibre displacements may be produced. In this method the displacements result from the formation of indentations 1 by pressing small round pointed tools into one of the surfaces of the plain paper to force out some of the fibres at corresponding places on the opposite side so as to produce there more" or less conical projections 2, each of which consists of displaced or loosed fibres. These indentations are preferably distributed uniformly at short intervals all over the surface of the paper; Fig. 1 shows the appearance of the indented side of such paper and gives an idea of the indentation sp'acifig preferred for paper, the thickness of which is about 5 to 6 mils. Referring more particularly to Fig. 2, which shows a cross-section of two Britain February 5, 1930 of the centres of fibre displacement, the displacement of fibres is greatest at the apex of each projection 2 and the displacement may be such as to produce a minute hole 3, as illustrated. It will be apparent that, if the impregnating oil on the side A of the paper is under a greater pressure than that on the side B, the displaced and loosened fibres of the projections 2 will be compressed and any small hole at the apex diminished in size and consequently the resistance to penetrations! at these places by the oil will be increased. On the other hand, if the oil on the side B of the paper is under a greater pressure than that on the side A, the displaced and loosened fibres of the projections will tend to become more dis- 7o in the accompanying drawing; various types of small pointed or rounded tools may be used to produce the desired fibre displacement and the spacing of the centres of the displacement may also be varied to meet different conditions.

After being prepared in the way indicated the 30 paper is cut into strips and applied to the cable by a spiral lapping in the usual way, as indicated in Figures 3 and 4. In Figure 3 the paper strips 4 are shown as provided with uniformly spaced projections. These are assumed to have been 35 prepared as described in connection with Figures 1 and 2 but are shown in both larger proportions and more widely spaced than would actually be the case in practice. These paper strips form the insulation which is wrapped on the conductor 5 and enclosed in the lead sheath 6.

The presence of the series of small projections distributed over the surface of the paper will have the additional effect of slightly separating each layer of paper from the next and thereby providing ease of fiow of oil longitudinally in the cable. The effect of the tension applied to the paper strips during lapping will be to deform the projections to a greater or less extent.

Accordingly by varying the tension applied to the paper, the separating space between any two consecutive layers can be controlled.

The presence of the differential flow resistance effect, dependent upon the direction of penetration of oil through the paper, can be utilized for the purpose of facilitating the impregnation of the cable insulation by the oil while assisting the retaining of the oil after impregnation has been completed. By arranging the paper with the indentations directed inwards towards the core the inward flow of the oil during impregnation will be facilitated and subsequent outward flow will be resisted; conversely, by arranging the paper with its indented surface nearer the core the impregnation of hollow cored cables may be facilitated by permitting the oil to flow from the hollow core outwards and subsequent inward fiow toward the core will be resisted. The presence of the small spacing effect between the layers due to the action of the projecting parts will have the additional efiect of assisting the longitudinal distribution of the oil during and after the process of impregnation. The cable insulation may be built up wholly of paper treated in the way indicated or it may be built up partly of such treated paper and partly of ordinary cable insulating paper according to the result desired to be obtained.

What I claim as my invention and desire to secure by Letters Patent is:-

1. An electric cable comprising an electric conductor, a sheath of insulating material sur rounding the said conductor and formed of a number of layers of paper at least some of which are of paper through which liquid or semi-liquid material may pass more easily in one direction than in the reverse direction, and liquid or semiliquid material impregnating the material of the said insulating sheath and occupying any interstices therein.

2. An electric cable comprising an electric conductor, a sheath of insulating material surrounding the said conductor and formed of a number of layers of paper in which paper groups of fibres round each of a plurality of centres are so displaced into positions which lie at an inclination with the normal plane of the paper that at each of such centres the passage through the paper of liquid or semi-liquid insulating material is facilitated in one direction more than in the converse direction, and liquid or semiliquid and insulating material impregnating the :ncsaaee material of the said sheath and occupying the interstices therein.

3. An electric cable comprising an electric conductor, a sheath of insulating material surrounding the said conductor and formed of a number of layers of paper which has on one side a plurality of indentations and on the other side corresponding tapering projections consisting of displaced and loosened fibres lying at an inclination with the normal plane of the paper, said indentations and projections together forming a plurality of valves facilitating the flow of liquid or semi-liquid insulating material therethrough in the direction from the first said side to the second'said side more than in the converse direction, and liquid or semi-liquid insulating material impregnating the material of the said sheath and occupying interstices therein.

4. An electric cable comprising an electric conductor, an insulating sheath surrounding the said conductor and formed of a plurality of wrappings of paper tape, and liquid or semi-liquid insulating material impregnating the material of the said insulating sheath and occupying interstices therein, the structure of the paper being such that the insulating sheath more readily permits the passage therethrough of liquid or semiliquid insulating material in one radial direction than in the converse direction.

5. An electric cable comprising an electric conductor, a sheath of insulating material surrounding the said conductor and formed of a number of layers of paper which at a pluralityof small areas distributed over the surface thereof is so modified in structure that at each of such areas liquid or semi-liquid insulating material may pass through the paper more easily in one direction than in the reverse direction, and liquid or semi-liquid insulating material impreghating the material of the said insulating sheath and occupying interstices therein.

HARRY HILL.

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